Carbon nanotubes are a class of cylindrical all-carbon molecules consisting of a rolled-up graphene sheet or coaxial sheets of rolled-up graphene. Single-wall carbon nanotubes (SWNTs), which have been a focus of considerable research, may exist in metallic, semi-metallic or semiconducting forms. The specific electrical properties of these single-wall carbon nanotubes are governed at a minimum by their specific (n-m) chirality indices and nanotube diameter. In addition, all varieties of carbon nanotubes possess advantageous mechanical and thermal properties over conventional materials.
Processes for aligning SWNTs are advantageous for taking full advantage of their properties. Alignment enhances electrical, thermal, and mechanical properties of SWNT materials, conveying properties of the SWNTs to fibers and films where the SWNTs are aligned. High-density arrays of vertically aligned SWNTs have recently been prepared on an alumina substrate coated with a thin layer of Fe catalyst. Nanotube growth takes place at the Fe catalyst layer by chemical vapor deposition from a carbon feedstock gas. The aligned SWNTs are oriented perpendicular to the plane of the alumina substrate. In general, the resulting yield of aligned SWNTs is less than 1% per unit mass of substrate material. Even for bulk synthesis of non-aligned SWNTs, such as the HiPco process, the SWNT yield is only about 30% per unit mass of substrate material.
In view of the foregoing, methods providing a high percentage yield of carbon nanotubes per unit mass of substrate material would be of substantial utility. Ideally, the method may be altered to preferentially produce SWNTs or multi-wall carbon nanotubes as individual filaments, rather than bundles which are typically obtained from HiPco production. Further, methods and substrate materials that provide for facile alignment of arrayed SWNTs or arrayed multi-wall carbon nanotubes would be of considerable interest as well.